The present invention pertains to the spark ignition art and, more particularly, to high energy electronic ignition system.
Spark ignition systems are well known, particularly in the automotive art. Such systems fall in basically one of three types:
(1) The conventional, or Kettering system; PA1 (2) capacitive discharge systems; and PA1 (3) inductive storage systems.
In the Kettering system, a magnetic field is built up in an ignition autoformer, or coil. At the time of ignition firing, current is interrupted whereby a high voltage spark is developed at the spark plug. The basic problem with the Kettering system is that the coil must be large and bulky in order to provide both the high voltage and high current required to sustain the flame front. This large size results in substantial capacitance at the coil secondary, whereby the rise time of the voltage at the spark plug is relatively slow. Thus, proper timing becomes a problem. Further, the size of the coil necessitates locating the coil at a remote location from the distributor whereby the two must be interconnected via a suitable cable. The cable results in an additional capacitance at the secondary of the coil, thus further degrading rise time of the pulse, as well as leading to engine faults through insulation degradation and to the generation of radio frequency interference.
A further problem with the Kettering system is its failure to maintain a high engine spark voltage at high RPM.
Finally, the Kettering system is relatively inefficient in that since it uses the coil as the main energy storing element, the coil must be current driven for a substantial time before it can develop sufficient magnetic field to create the required spark. Thus, there are significant coil I.sup.2 R losses.
The capacitive discharge ignition attempts to overcome some of the shortcomings of the Kettering system. Here, a capacitor is charged to a voltage higher than that normally developed at the primary of the Kettering system, whereby at firing the capacitor is switched to the primary of the coil. Since the voltage of the primary of the coil is higher with this system, the coil need require fewer secondary turns thus reducing its secondary capacitance and allowing faster rise times. Further, the coil may be charged to a voltage such that its stored energy will maintain a high spark energy over increasing RPM. A primary disadvantage to the capacitive discharge ignition system is that it still requires a relatively large ignition coil, thus suffering the disadvantages described above. Moreover, the energy stored in the capacitor, as transformed through the ignition coil, is generally not sufficient to maintain a long burn time such as is normally required for efficient engine operation in lean burned type engines.
Finally, considerable work has been done with inductive storage, or transistor aided type ignition systems. Here, a transistor replaces the points of the standard Kettering system and logic circuitry controls the dwell time such that at higher RPM the percent dwell increases, thereby maintaining a substantially high spark energy. The principle problem with these systems are similar to those shared by the Kettering system, namely the need for a large ignition coil and its attendant problems, including inefficiency.
It should also be mentioned that with respect to the capacitive discharge ignition system and especially the inductive storage system, elaborate schemes have been developed to control these systems such that a constant spark energy is maintained as a function of RPM. Thus, cost and reliability are serious drawbacks of such systems.
A further problem with ignition systems of all of the above described type is that they require a mechanical distributor to properly distribute the high tension sparking voltage to the various spark plugs of a multicylinder engine. Such mechanical distributors are, of course, subject to wear and must be frequently maintained to provide optimum operation and engine efficiency.
The development of more elaborate ignition systems has resulted from the requirement for higher engine efficiency as well as lower engine produced pollution. It has been found that by producing a relatively long duration, controlled energy spark, more of the gas air mixture in the cylinder can be burned thus increasing engine efficiency and reducing hydrocarbon pollutants.